In some methods of constructing floors and roofs, steel joists are placed in position spanning structural supports therefor. The joists support panels, such as plywood sheets, which form the bottom member of a mould, and concrete is poured on the panels to form a slab. It is desirable to be able to reuse the panels after the concrete has hardened and the forms removed. This requires that the forms be supported in such a way that they can be removed with little or no damage to them, and the prior art teaches a variety of techniques for supporting forms in such a way that they can be removed. However, some of the methods are not applicable to open web joist systems; some, which may be used with open web joist systems, are difficult to use in practice; some of the systems may raise safety questions; and some of these systems may not permit an extensive span between adjacent joists.
In one type of system, metal bars, referred to herein as spanner bars, extend between adjacent joists and provide support for the concrete forms. The prior art methods of supporting the spanner bars at the joists, especially at open web joists, can present problems in assembly, disassembly, adjustability, adaptability to a variation in joist structure, and safety.